At approximately 18:00 on December 18, 2014, I was in the village of South Strafford, Vermont, USA (42.84°N, -72.36°W) and was alerted by a group of children as to the presence of what they believed was an injured owl on a picnic table in the school playground. They suspected it was injured because it did not fly away when they approached it. Upon investigation, I discovered a Barred Owl (Strix varia) standing on a picnic table. It did not flush as I approached to within 2 m, instead bowing its head and spreading its wings in a mantling posture (Fig. 1). The bird did not appear injured, although I noted a large number of feathers scattered on the table. On closer investigation, however, I observed that the owl was perched on the carcass of a second Barred Owl, which it had been plucking and consuming (Fig. 2). The carcass was intact except for the chest and abdomen, which had been torn open, and was readily identifiable as a Barred Owl. After verifying the identity of the carcass, I left the area to avoid disturbing the individual further. Whether this observation reflects predation or scavenging is unclear. Barred Owls subsist primarily on small mammals, but are opportunistic foragers with a broad dietary niche . Scavenging has been documented only once, with camera traps providing evidence of Barred Owls feeding on a road-killed Eastern Gray Squirrel (Sciurus carolinensis) and a heavily decomposed White-tailed Deer (Odocoileus virginianus) in North Carolina . Although records of Barred Owl scavenging on a conspecific are lacking, it seems reasonable to assume that they would do so if given the opportunity.
Evidence that Barred Owls are predators of other owls is equally scarce. Johnsgard  suggested that Barred Owls were occasional predators of Eastern Screech-Owl (Megascops asio) and perhaps even Long-eared Owl (Asio otus), although the latter record appears to be based on stomach contents and not direct observation of a predation event. Leskiw and Guttierez  observed a Barred Owl with feathers of a Northern Spotted Owl (Strix occidentalis) in its talons and found nearby a fresh carcass of a Northern Spotted Owl. The forest floor around the carcass was disturbed, as though a struggle had occurred, and a necropsy of the Northern Spotted Owl suggested the cause of death was penetrating trauma of the chest and abdominal cavities resulting in lacerations of the heart, lungs, and liver. Puncture wounds consistent with an attack by a Barred Owl were found during the necropsy. The authors found no evidence of fractured bones, as might be expected if death was the result of predation by a mammal. Barred Owls compete with Northern Spotted Owls for territorial space  and thus the putative attack could have represented either territorial aggression or a predation event.
Perhaps even more surprisingly, Graves and Niemi  reported an observation of a Barred Owl carrying the carcass of a Great Gray Owl (Strix nebulosa), a species that can be substantially more massive than a Barred Owl. The authors believed that the Great Gray Owl had been killed recently based on the lack of rigor mortis and argued that evidence at the scene was consistent with predation by the Barred Owl.
Although anecdotal, two comments posted to a blog that I wrote about this incident indicate that Barred Owls will depredate conspecifics. One commenter wrote on March 10, 2015:
"My wife and I saw a barred owl attack and eat another barred owl right next to our bird feeders yesterday evening, around sunset. It was quite a shock. We think it was probably starvation, not territory protection, because the victor carried off the loser after tearing it up a bit. This was in central Vermont, in a wooded rural area. We’d been seeing barred owls hanging around the feeders recently, and just the day before had seen one catch a mouse in the snow. But we never expected to see cannibalism." Mark Alexander
Another commenter wrote on March 15, 2015:
"I just found a similar situation in Williston. Walking through the woods, I spooked a larger barred owl that had a smaller barred owl in its talons. It ended up dropping its prey/meal. One wing and the head were missing." Will S.
I lack sufficient evidence to determine whether the incident that I observed reflected scavenging or the outcome of intraspecific predation. The picnic table on which the carcass was located was approximately 5 m from a two-lane road with a posted speed of 25 mph, suggesting the possibility that the individual was killed in collision with a motor vehicle and later scavenged. Road-kill is a common source of mortality among Barred Owls . Another possibility is that the individual died of starvation or disease before being scavenged, although starvation is somewhat unlikely given the timing of the incident in early winter and that the winter up to that point had been fairly mild. Snowdepth at the time of the observation was approximately 20 cm, but most of that snow had fallen within the past week and prior to that the ground had remained largely bare. Although the circumstances of this observation remain unresolved, it does demonstrate clearly that Barred Owls are opportunistic foragers that, given the opportunity, will consume conspecifics.